cli-test: Path separation compatible with Windows — heartwood

Running tests on Windows requires separating the path to executables by ;.

 impl TestFormula {
     pub fn new(cwd: PathBuf) -> Self {
         #[cfg(windows)]
         const PATH_SEPARATOR: char = ';';
         #[cfg(not(windows))]
         const PATH_SEPARATOR: char = ':';
         Self {
             cwd: cwd.clone(),
             env: HashMap::new(),

             subs: Substitutions::new(),
             bins: env::var("PATH")
                 .map(|env_path| {
                     let mut bins: Vec<PathBuf> = env_path.split(':').map(PathBuf::from).collect();
                     let mut bins: Vec<PathBuf> =
                         env_path.split(PATH_SEPARATOR).map(PathBuf::from).collect();
                     // Add current working directory to `$PATH`,
                     // this makes it more convenient to execute scripts during testing.
                     bins.push(cwd);